From decay channels of these resonances \(X_{0(1)}\rightarrow \)  \(D^{-}K^{+}\) ,
it is evident that they are built of four different valence quarks \(ud\overline{s}\overline{c}\) . These circumstances place \(X_{0}\)  and \(X_{1}\)  to
distinguishable position in the \(XYZ\)  family of exotic mesons. The LHCb's
discovery is doubly remarkable, because existence of the resonance \(X(5568)\) , seen by the D0 collaboration [1]} and presumably composed of
quarks \(sd\overline{b}\overline{u}\) , was not later confirmed by other
experiments.
